As discussed in the applicant's (TruePosition's) submission to the 3rd Generation Partnership program (in 3GPP TR 45. 811 R6) and again in the UMTS UE location standard (e.g. 3GPP TS 25.305 R 7.1.0), uplink time-difference-of-arrival (U-TDOA) is particularly well suited to UMTS due to selection of the Wideband Code Division Multiple Access (W-CDMA) direct sequence spread spectrum radio air interface.
As taught in the well-known Cramer-Rao bound statistical theory, the accuracy of the location estimation is limited by several practical factors such as integration time, signal-to-noise ratio (SNR) at each receiver site, as well as the bandwidth of the transmitted signal. The higher power level (Eb/No) associated with the lower spreading factors of a CDMA-based wireless communications network provides a high level of accuracy because many LMUs can participate in the location effort.
The UMTS WCDMA-based system has an uplink signal (mobile (user equipment (UE)) to base station (NodeB)) that uses a direct sequence spread spectrum and contains two distinct, separate code multiplexed channels so that the cycling of the UE's transmitter power does not cause electromagnetic interference to the audio output(s) of the UE.
The dual uplink channels (dual channel quadrature phase shift keying (QPSK)) are achieved by applying the coded user data to the “I” or In-phase input to the QPSK modulator, and control data which has been encoded using a different code to the “Q” or quadrature input to the modulator. The resulting physical uplink channels are called the Dedicated Physical Data Channel (DPDCH) and the Dedicated Physical Control Channel (DPCCH).
TruePosition's commercially deployed Wireless Location System (WLS) uses geographically distributed receivers called Location Measurement Units (LMUs) deployed as standalone, co-located with the UMTS base station (a Node-B) or integrated into the NodeB. The LMUs are used to collect the uplink radio signal and then the WLS uses TOA, TDOA, AoA, PDOA or a combination of techniques is used to calculate a location for the wireless device.
The inventive techniques and concepts described herein apply to code-division radio communications systems such as the Universal Mobile Telecommunications System (UTMS), which is also known as W-CDMA. The UMTS model discussed above is an exemplary but not exclusive environment in which the present invention may be used.